1. Field of the Invention
The present invention relates to a cycloolefin-based polymer compound and a method of preparing the same. More particularly, the present invention relates to a cycloolefin-based copolymer which is prepared from a monomer which may be easily and economically obtained by hydrogenating dicyclopentadiene that occupies much of C5 fractions from naphtha cracking or a monomer which may be obtained by chemically bonding three molecules of cyclopentadiene using a Diels-Alder reaction and then hydrogenating the cyclopentadiene, and to a hydrogenation process.
2. Description of the Related Art
Whereas C4 or less fractions from naphtha cracking are separated and purified and are thus useful in the petroleum industry, C5-fractions thereof are mostly burned and used as fuel and only a little thereof is separated and purified and thus industrially applied by some manufacturers. Hence, thorough research into the separation and purification of C5-fractions so as to prepare high value-added chemical products is ongoing.
In particular, cyclopentadiene occupies much of C5-fractions. Cyclopentadiene spontaneously undergoes a Diels-Alder reaction at room temperature and is thus converted into dicyclopentadiene. In order to manufacture plastics from dicyclopentadiene, copolymerization of dicyclopentadiene with ethylene, alpha-olefin or styrene is under active study (Scheme 1). Dicyclopentadiene has two olefin groups, of which the olefin group of carbons at the 5-6 positions is known to be more greatly reactive than the olefin group of carbons at the 2-3 positions. Upon copolymerization of dicyclopentadiene with a vinyl monomer using a polymerization catalyst, the olefin group of carbons at the 5-6 positions first reacts and thus a polymer at the intermediate step of Scheme 1 is obtained, but the reaction does not typically stop at this step and is further carried out and thus the olefin group of carbons at the 2-3 positions, which remain in the polymer, additionally participates in the polymerization, resulting in a crosslinked polymer (Naga, N. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 1285-1291). However, the crosslinked polymer is difficult to process and limitations are imposed on developing the end uses thereof.
Group IV metallocene catalysts were reported to enable the preparation of the uncrosslinked polymer at the intermediate step of Scheme 1 provided that the amount of dicyclopentadiene was adjusted to be less than 10% (Simanke, A. G.; Mauler, R. S.; Galland, G. B. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 471-485; Suzuki, J.; Kino, Y.; Uozumi, T.; Sano, T.; Teranishi, T.; Jin, J.; Soga, K.; Shiono, T. J. Appl. Polym. Sci. 1999, 72, 103-108). Recently, group III metal-based catalysts have been reported to enable the preparation of copolymers including dicyclopentadiene in a large amount because only the olefin group of carbons at the 5-6 positions is reactive and the olefin group of carbons at the 2-3 positions is not reactive (Journal of Organometallic Chemistry 691 (2006) 3114-3121; Xiaofang Li and Zhaomin Hou, Macromolecules 2005, 38, 6767-6769; Xiaofang Li, Masayoshi Nishiura, Kyouichi Mori, Tomohiro Mashiko and Zhaomin Hou, Chem. Commun., 2007, 4137-4139). However, because such polymers have an olefin group that is unreactive to the molecular structure, they are problematic in terms of direct commercial use. An olefin group having high reactivity may cause the deformation of resins upon melting and may decrease durability. For these reasons, the use of resins of the polymer chain including the olefin group is not common in the industrial world.
Resins resulting from hydrogenating linear polymers produced via ring-opening metathesis polymerization (ROMP) of the olefin group of carbons at the 5-6 positions of dicyclopentadiene as shown in Scheme 2 below have been produced in the market by Zeon, Japan (Masahiro Yamazaki, Journal of Molecular Catalysis A: Chemical 213 (2004) 81-87). In this case, it is necessary to completely remove the double bonds of the resin by hydrogenation. However, it is not easy to hydrogenate all of the double bonds into single bonds for polymer compounds having olefin groups.

On the other hand, dicyclopentadiene may be converted into cyclopentadiene at high temperature, and then subjected to a Diels-Alder reaction with ethylene or alpha-olefin thus preparing a norbornene-based cycloolefin which may then be copolymerized with ethylene (Cho, E. S.; Joung, U. G.; Lee, B. Y.; Lee, H.; Part, Y.-W.; Lee, C. H.; Shin, D. M. Organometallics 2004, 23, 4693-4699; Lee Si-Geun, Park Yeong-Hwan, Hong Seong-Don, Song Gwang-Ho, Jeong Bung-Gun, Nam Dae-U, Lee Bun-Yeoul, Korean Patent No. 10-0458600 (2004. 11. 16); Incoronata Tritto, Laura Boggioni, Dino R. Ferro, Coordination Chemistry Reviews 250 (2006) 212-241). The copolymer thus prepared is called a cycloolefin copolymer (COC) (Scheme 3). As represented in the bottom of Scheme 3, the norbornene-based monomer may also be prepared into a resin by ROMP and then hydrogenation (Mashahiro Yamazaki, Journal of Molecular Catalysis A: Chemical 213 (2004) 81-87). The polymer thus obtained is referred to as a cycloolefin polymer (COP). Due to the reasons it is difficult to hydrogenate the polymer compound mentioned above, the cycloolefin copolymer (COC) is more favorable in terms of preparation process than is the cycloolefin polymer (COP). Furthermore, when the ratio of ethylene and norbornene of COC is adjusted, the glass transition temperature (Tg) of the resin may be controlled, making it possible to prepare products of various grades, and also, COC is advantageous because of high transparency, low birefringence, and low resin density, and thus the end use thereof has been developed in fields including packaging materials of food and medicines, DVD materials, and optical films for displays.

However, because COC resins prepared using norbornene comprise a large amount of norbornene monomer, high-Tg resin grades are brittle and thus unsuitable for use in optical films. With the goal of overcoming drawbacks of the properties of COC resins generally prepared from norbornene including the above problems, attempts have been made to use, as a COC monomer, a bulky cycloolefin compound such as 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphtalene (hereinafter, abbreviated as “DMON”) obtained by subjecting norbornene once more to a Diels-Alder reaction with cyclopentadiene (Scheme 4; W. Kaminsky, Catalysis Today 62 (2000) 23-34). In order to improve the properties of COP, a lot of effort is directed to the preparation of resins by ROMP and hydrogenation of DMON as represented in the bottom of Scheme 4 (Masahiro Yamazaki, Journal of Molecular Catalysis A: Chemical 213 (2004) 81-87). The use of a bulky cycloolefin monomer upon synthesis of COC enables a high-Tg resin to be prepared from a polymer including ethylene in a comparatively larger amount than when using norbornene to prepare COC. The problems related to brittleness noted above may be overcome because the polymer chain includes more of the flexible ethylene monomer than it does the cycloolefin monomer. However, as shown in Scheme 4, DMON which is prepared via two steps from dicylcopentadiene is problematic because its preparation process is not easy, and thus it is considerably expensive and unsuitable for use as a polymeric monomer. Hence, the economic preparation of DMON is currently regarded as important to the commercialization of DMON-based resins.

Furthermore, the polymer material at the bottom of Scheme 4 was commercialized by Zeon.
On the other hand, cyclopentadiene is a material that occupies much of C5 fractions. Cyclopentadiene (CPD) spontaneously undergoes a Diels-Alder reaction at room temperature and is thus converted into dicyclopentadiene (DCPD). Additionally, dicyclopentadiene may be further subjected to a Diels-Alder reaction with cyclopentadiene, thus preparing tricyclopentadiene (TCPD). These reactions may continue, and thus the use thereof to prepare resins is possible in the industrial world (Scheme 5, Chemical Engineering Science 56 (2001) 927-935).

Such cyclopentadiene (CPD) Diels-Alder reaction products have two olefin groups. One olefin group is in the form of a norbornene compound (hereinafter, referred to as “norbornene-type olefin”), and the other olefin group is in the form of cyclopentene (hereinafter, referred to as “cyclopentene-type olefin”). Typically, of two olefin groups, norbornene-type olefin is known to be the more reactive. There were reported methods of preparing 5,6-dihydrodicyclopentadiene by selectively hydrogenating only the norbornene-type olefin among two olefin groups of dicyclopentadiene using a difference in reactivity between two olefin groups.
For example, synthesis of 5,6-dihydrodicyclopentadiene via selective hydrogenation of dicyclopentadiene using a commercially available Pd/alumina or Pd/C catalyst is disclosed in U.S. Pat. No. 7,078,577, Inorg. Chem. 1999, 38, 2359 and J. Org. Chem. 1991, 56, 6043. In order to attain the hydrogenation selectivity in the presence of such a catalyst, hydrogen is essentially required to be added in an equivalent quantity. Because the norbornene-type olefin group among the two olefin groups has a faster reaction rate in the presence of the above catalyst, it is first hydrogenated. If hydrogen is added in an amount above the equivalent quantity, the cyclopentene-type olefin group having a slow reaction rate may also be hydrogenated, so that tetrahydrodicyclopentadiene is formed as a by-product. Specifically, because selectivity is adjusted by the reaction rate, even when a continuous process is developed in consideration of reaction conditions sensitively affecting the selectivity and thus the reaction conditions are efficiently controlled, it is inevitable that unreacted dicyclopentadiene remains to some degree (<0.3%), and a by-product tetrahydrodicyclopentadiene is formed in an amount of 3% or more.
Moreover, results of selectively hydrogenating dicyclopentadiene using, as a catalyst, nickel metal obtained by reducing nickel acetate with NaBH4 within a reactor were reported in Tetrahedron Letters 2007, 48, 8331. Even in this case, hydrogen was added in 1.1 equivalents in order to attain the selectivity, and the reaction product was purified using recrystallization in order to remove the by-product tetrahydrodicyclopentadiene. Also, results of selective hydrogenation of tricyclopentadiene using, as a catalyst, nickel metal obtained by reducing nickel acetate with NaBH4 within a reactor were reported in J. C. S. Perkin I, 1977, 19. Even in this case, hydrogen was added in 1 equivalent in order to attain the selectivity, and 0.360 g of nickel acetate was used to hydrogenate 1.5 g of tricyclopentadiene but its catalytic activity was inappropriately low for commercial use.